A high-speed data communication system such as a DTV broadcast communication system requires linear equalization for optimum performance and signal coverage. Because of the high data rates required in a DTV system, an adaptive equalization system becomes very difficult to implement using known equalization techniques.
Traditional linear equalization (compensation) for television systems has been accomplished by analog, pre-distortion equalizers which are static (non-adaptive). These equalizers are filters/correctors that require factory adjustments to provide a desired amount of pre-distortion (pre-equalization). Aging of the filters/correctors and temperature change cause drift in the amount of pre-distortion. Occasional field adjustments are required.
Digital signal processing techniques provide improved performance of the pre-equalization of the information signal. Specifically, digital signal processing can be used in an adaptive correction and equalization approach. Such an adaptive approach can eliminate the factory and field adjustments.
It is known to perform adaptive correction of a signal within a signal stream proceeding toward a transmitter. However, in a relatively fast data rate system, the correction requires a relatively large amount of processing in a short period of time. For example, assuming a 64 tap Finite Impulse Response ("FIR") filter, processing a DTV signal at a 25 Mhz sample rate, the update of the filter requires 64 times 25 million updates per second. This translates to 1.6 billion updates per second. Such an update rate requires that the adaptation process be done offline.